Sketchpad, developed by Ivan Sutherland in 1963, is a pioneer of CG/CAD systems that revolutionized the way computers interact with humans. With the technological development of computers, CG/CAD has become not only a medium for visualizing physical simulations of light, rigid bodies, and fluids in the real world, but has also invented unique expressions in games, art, and movies in the virtual world. This lecture will focus on the mathematical understanding of 2D/3D CG/CAD and its practical application with general-purpose algorithms, taking into account such advanced applications.